Method of contouring the recording surface of a magnetic head transducer

ABSTRACT

A method of contouring a recording and/or playback surface of a magnetic head transducer to form a precisely contoured surface having a one inch radius of curvature along its major axis is described. The head is secured to a flat surface of a cone-shaped holder and the holder and head are placed within a hemispherical transfer block having a concave surface with a one inch radius of curvature so that the recording surface is in abutting relationship with the concave surface. The holder and head are then placed in a rotatable hemispherical grinding apparatus having a concave grinding surface with a one inch radius of curvature so that the recording surface of the head is disposed in abutting relationship with the concave surface of the grinding tool and is ground to the desired one inch radius of curvature. To further refine the contour of the recording surface, the holder and head are then transferred to a hemispherical polishing apparatus with a concave polishing surface having a one inch radius of curvature and the head is polished to remove irregularities on the recording surface. This method of shaping the recording surface of a head transducer yields uniformly contoured surfaces for large quantities of magnetic head transducers and provides high performance heads which are suitable for high density digital and video recording systems wherein close tolerances are desired.

BACKGROUND OF THE INVENTION

This invention relates to magnetic head transducers and in particular tomagnetic head transducers having precisely contoured recording surfaces.

In recording or reading information on a moving information storagemedia, such as a magnetic recording disc, relative motion between amagnetic head transducer used for reading and writing information andthe storage media on which information is written on and read from isrequired. The relative velocity between the head and media interface maybe, for example, 550 IPS for video and high density digitalapplications. To achieve maximum performance, an interface of intimatecontact is provided between the head and media surface withoutdestruction or excessive wear of the magnetic flux responsive coating onthe surface.

As contact pressure between the head and media is increased to improveperformance, both media and head wear are increased. The problem isparticularly severe in video applications and compounded with the mediasutilized for storing single video frames on separate tracks of amagnetic disc wherein one track at a time is continuously in contactwith the head to provide a continuous stationary display of a singleframe. In only five minutes of playtime revolving at 3600 RPM, forexample, a track on the disc is scraped about 18,000 times by the head;the by-products are so hard and abrasive that the same materials arecommonly used as a lapping compounds.

To prevent failure caused by contact between the head and disc,lubricated surfaces and/or air film separations have been used. However,any separation between the head and disc caused by such lubricationfluid or air film imposes a loss of signal and hence performance. Ahead/disc separation equal to one wave length could cause about 54.6 dBloss in the output of the replay head. Since it is desired to recordwave lengths that approach 1.75 microns, the playback head voltage isreduced to 50% by only 0.19 micron of separation. On the other hand, asdiscussed above, reduction of separation to meet desired preformancewould cause the interface to be destroyed within a few seconds.

Prior art solutions to the head-to-disc interface problem have generallybeen of two types: flying heads in conjunction with rigid hard-surfacediscs and heads having large surface areas buried in soft flexible"floppy" discs. Flying head discs are very expensive and requirecomplicated and expensive recording/playback systems. A flexible orso-called "floppy" disc reduces the handling and cost problems incurredin the flying head rigid-disc system. Some record/read heads for"floppy" discs are relatively large to provide an interface comprised ofa large contoured head buried in the soft flexible media. The largerecord/read head surface area distributes the force per unit area toreduce media wear and separation loss. As the media is moved past thehead, however, air collects between the head and disc surface to form anair film. The thickness of this air film is a function of head and mediasurface finishes, media stiffness, head-media penetration, head size,head surface contour, viscosity of the air and disc-head relativevelocity. Because of these restraints, most flexible or "floppy" discapplications are limited to slow speed, low bandwidth digital computerapplications or voice recording systems.

In high performance recording systems the shape of the magnetic headtransducer is important in achieving optimum system performance.Copending Patent Application Ser. No. 45,528, filed of even date withand assigned to the Assignee of the present invention, describes theadvantages obtained from using a head having a one inch radius ofcurvature on the recording surface thereof in achieving intimate head todisc contact to optimize signal transfer between the head and disc whilemaintaining sufficient separation therebetween to minimize wear. Becauseclose tolerances of the dimensions of the head are important, precisecontouring of the recording surface of the head must be achieved. Priorart techniques for shaping the recording/playback surface of the headhave generally involved the use of abrasive tapes of varying degrees ofabrasiveness to grind and polish the head. The most abrasive tapes areused to grind the head while the less abrasive tapes are used to polishthe head and further refine the contouring. One problem encountered withthis method is that the amount of penetration of the tape into thevarious heads often varied from head to head, thereby producing headswith non-uniform contours.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide animproved technique for storing information on a flexible storage media.

Another object of the invention is to provide an improved system formagnetically storing information on a flexible magnetic recording disc.

It is another object of the invention to provide an apparatus whichpermits the precise recording and reproducing of wide bandwidth signalssuch as video signals and narrow bandwidth signals such as digitalsignals using inexpensive flexible particulate-type recording mediacartridges.

A still further object of the invention is to provide an improved systemfor recording and reading information on a flexible information storagemedia over a wide range of vertical head alignments and specialgeometries.

Yet another object of the invention is to provide a relatively thinflexible magnetic recording media cartridge system with an improveduniform head-to-media coupling profile.

Still a further object of the invention is to provide a head transducerwith a precise one inch radius of curvature along its recording/playbacksurface.

Yet another object of the invention is to provide an improved method ofcontouring a recording/playback surface of a magnetic head transducer.

Still another object of the invention is to provide an inexpensivemethod of contouring a recording/playback surface of a magnetic headtransducer.

Still a further object of the invention is to provide a method forproducing large quantities of heads having uniformly contouredrecording/playback surfaces.

These and other objects are accomplished in accordance with the methodof the present invention. The head transducer having a relatively flatrecording/playback surface is affixed to a holder means, which isinserted in a positioning member having a concave surface with apredetermined curvature equivalent to the desired curvature of therecording/playback surface. The head and holder are adjusted until therecording/playback surface is in abutting relationship with the concavesurface. The holder and head are then transferred to a shaping apparatushaving a concave surface with a curvature equivalent to the desiredcurvature of the head. The recording/playback surface is positioned inabutting relationship with the concave surface of the shaping apparatusand the recording surface is mechanically shaped thereby to form thedesired contour. In one embodiment the shaping apparatus is comprised ofa grinding apparatus having a rotatable concave grinding surface forinitially contouring the recording/playback surface of the head and apolishing apparatus having a rotatable concave polishing surface forfurther refining the contoured surface. During both the grinding andpolishing operations, the holder means is positioned so that the head isin abutting relationship with the concave surfaces of the grinding andpolishing apparatus, the concave surfaces of both apparatus having acurvature equivalent to the desired curvature of a recording surface. Inanother embodiment spacer means is provided for properly locating theholder means and head in the positioning member. The spacer means isplaced beneath the holder means for adjusting the orientation of thehead with respect to the concave surface. Further adjustment of the headis obtained by moving the head with respect to the holder means.

In a preferred embodiment the radius of curvature of the concavesurfaces of the positioning member, the grinding apparatus and polishingapparatus are essentially one inch, which is equivalent to the desiredcurvature of the recording/playback surface along a major axis thereof.The holder means has a polyhedral shape with a plurality of flatsurfaces formed thereon, each of said flat surfaces being disposedorthogonally with respect to at least one of the other flat surfaces.Each of the flat surfaces accommodates one head transducer so that aplurality of heads can be contoured at the same time to ensure that theheads shaped using this method have precisely contouredrecording/playback surfaces and are suitable for high density digitaland video systems, wherein precise dimensions are critical for effectiveperformance. This method is also well suited for shaping largequantities of heads to form uniform contours.

BRIEF DESCRIPTION OF THE DRAWINGS

Still further objects and advantages of the invention will be apparentfrom the detailed description and claims when read in conjunction withthe accompanying drawings wherein:

FIG. 1 is a perspective view of the information storage system of thepresent invention;

FIG. 2a is a block diagram of the electronic control system for theinformation storage system shown in FIG. 1;

FIG. 2b is a block diagram of the components of a single chipmicrocomputer contained in the electronic control system of the presentinvention;

FIGS. 3a-3e show various views of a recording cartridge and magneticrecording disc of the present invention;

FIGS. 4a and 4b are perspective views of the upper and lower members ofa cartridge holder of the present invention;

FIGS. 5a and 5b are perspective views of the cartridge holder positionedin the deck of the information storage system;

FIG. 6 is a bottom elevational view of the cartridge holder with arecording cartridge positioned therein showing the points of engagementof a motor rotational means with a central hub member affixed to themagnetic recording disc;

FIG. 7 is a top perspective view of a magnetic head transducer and ahead positioning apparatus of the information storage system of thepresent invention;

FIGS. 8a-8c are front elevational views of a shutter and mask assemblyused to determine the position of the magnetic head transducer withrespect to the disc;

FIG. 8d is a perspective view of the optoelectronic system used todetermine the position of the head transducer;

FIGS. 9a and 9b are side elevational and top plan views, respectively,of the magnetic head transducer with a ramp member attached thereto;

FIGS. 10a-10c depict various views of the magnetic head transducer ofthe present invention;

FIGS. 11a and 11b are perspective views of the components comprising themagnetic head transducer of the present invention;

FIGS. 12a and 12b are cross-sectional views of a positioning apparatusand a grinding apparatus, respectively, for shaping the recordingsurface of the magnetic head transducer;

FIG. 13 is a top plan view of the magnetic recording disc of the presentinvention showing the disc divided into four annular quadrants;

FIG. 14 is a block diagram of the system used to vary the amount ofwrite current supplied to the magnetic head transducer;

FIG. 15 is a block diagram of the system used to position the headtransducer with respect to the magnetic recording disc;

FIG. 16 is a graph showing the various electrical signals generated bythe components of the head positioning system of FIG. 15;

FIGS. 17a and 17b are graphs showing the velocity of the head transduceras a function of the displacement along the disc;

FIG. 18a is a block diagram of the system used for erasing informationfrom the disc;

FIG. 18b depicts the various electrical signals generated by theinformation erasing system of FIG. 18a;

FIG. 18c shows the relative positions of the head transducer withrespect to the center line of a recording track where information isbeing erased;

FIG. 19a shows bottom elevational views of a recording cartridge and ahead cleaning cartridge used in the information storage system of thepresent invention;

FIG. 19b depicts front end views of the recording and head cleaningcartridges of FIG. 19a; and

FIG. 19c is a block diagram of the system used for cleaning debris andother contaminants from the head transducer.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

The invention will be described in conjunction with a complete storagesystem for storing information on a magnetic recording disc. Theinformation storage system described herein is preferably a high densitydigital information system suitable for storing large quantities ofdigital information in a small area.

General Description of the Information Storage System

Referring to FIG. 1, cartridge 11, cartridge holder 12 and deck 13 areshown in perspective. Cartridge 11 is comprised of upper and lowercartridge members 11a and 11b, respectively, which snap together to forma protective housing for a flexible magnetic recording disc (not shown)contained therein. Holder 12 includes upper and lower holder members 12aand 12b which snap together to form a holder assembly for cartridge 11.Holder 12 is normally mounted in deck 13 by the engagement of extensionmembers 15 (one of which is shown in FIG. 1) with vertical slots 16.During system operation, cartridge 11 is inserted into holder 12 throughopen end 14. Deck 13 functions as a base member for the informationstorage system and includes means for rotating the disc and reading andwriting information thereon. When cartridge 11 and holder 12 areproperly located in deck 13, openings 17, 18 and 19 are aligned withrespective openings (not shown) in lower holder member 12b and in lowercartridge member 11b, thereby providing access to the magnetic recordingdisc for a magnetic head transducer and a rotational means such as adrive motor to engage the magnetic recording disc through openings 17and 18, respectively.

Upper cartridge member 11a and upper holder member 12a include openings20 and 21, respectively, which are in registration with opening 19 andand corresponding openings (not shown) in lower cartridge member 11b andlower holder member 12b when cartridge 11 and holder 12 are properlypositioned in deck 13. A light emitting diode 22 is mounted in opening21 for transmitting light energy through openings 20 and thecorresponding opening in lower cartridge member 11b. A phototransistor23 detects the rate at which light energy bursts emanate from cartridge11 to determine the speed of rotation of the magnetic recording disc.Precise location of cartridge 11 with respect to openings 17, 18 and 19of deck 13 is essential for effective operation of the system.Specifically, precise alignment of cartridge 11 in deck 13 is requiredfor proper head-to-disc contact and for accurate positioning of the headon various tracks of the disc and also to permit the motor rotationalmeans to engage the disc. Holder 12 includes means for maintainingcartridge 11 in a fixed position therein. Such means include springs 24mounted on the upper holder member 12a for exerting downward pressure oncartridge 11 to hold cartridge 11 in a fixed position. Similarly, deck13 includes means for properly aligning holder 12 and cartridge 11 andmaintaining them in a fixed position. Such means include support members25 and alignment posts 26. The means used for accurately and preciselylocating the magnetic recording disc with respect to the head and motorrotational means are described in more detail below.

Located on the reverse side of deck 13, but not shown in FIG. 1, are themagnetic head transducer, motor rotational means, and the centralcontrol system for the information storage system. FIG. 2a shows thecentral control system and the interface with a host machine such as acomputing apparatus from which information signals and commands aregenerated. The heart of the control system is digital processor 27,which is preferably a microcomputer of the TMS 1000 type, manufacturedand sold as a standard product by Texas Instruments Incorporated andincluding a read-only-memory 27a, a random-access-memory 27b and anarithmetic logic unit 27c on a single semiconductor chip as shown inFIG. 2b. Digital processor 27 receives various command and data signalsfrom host machine 28 and transmits various return signals to hostmachine 28 via interface 29. Digital processor 27 further includes meansfor preventing information signals from being transmitted to magnetichead transducer 30 by host machine 28. Digital processor 27 moves head30 from one track location to another on the recording disc byselectively controlling a head positioning system 31 and receives asignal indicative of the position of recording head 30 at any given timefrom head positioning system 31. Head positioning system 31 includes alinear servomotor system for linearly moving head 30 across the disc andan optoelectronic system for providing feedback information on theactual position of recording head 30. Similarly, host machine 28selectively activates motor rotational means 32 via motor controller 33for providing rotational motion to the magnetic recording disc duringthe reading and writing of data on the disc. Digital processor 27controls rotational means 32 when head 30 is being repositioned on disc37. A separate optoelectronic system, including diode 22 andphototransistor 23, provides real time information indicative of therotational speed of the magnetic recording disc. Data to be stored onthe magnetic recording disc is transmitted as an information signal fromhost machine 28 to head 30 for storage on the disc. Data read from thedisc by magnetic recording head 30 is transmitted back to host machine28 via interface system 29. The operation of the control and interfacesystem is described in further detail below.

Cartridge and Magnetic Recording Disc

The contents of cartridge 11 including the magnetic recording disc areshown in FIGS. 3a through 3d. Upper cartridge member 11a and lowercartridge member 11b of cartridge 11 are substantially rectangular inshape and include rectangular extension portions 35 which form 90 degreeangle surfaces 36. Magnetic recording disc 37 is preferably of circularshape and is comprised of flexible plastic or film material with amagnetic flux-responsive coating positioned thereon. Disc 37 includes aplurality of information storage tracks concentrically arranged atpredetermined distances thereon. The distance between the centerlines ofadjacent tracks is preferably 0.254 mm (10 mils). During systemoperation, head 30 writes information on and reads information fromselected tracks of disc 37. Hub 38 is affixed to the central portion ofdisc 37 for engaging motor rotational means 32 and transferringrotational motion to disc 37. Hub 38 further includes a latch member 39projecting radially inward from projection member 40 for engaging acorresponding latch member on motor rotational means 32, as described inmore detail below with reference to FIG. 6.

Also included in the central region of disc 37 are a plurality ofopenings 41 which are concentrically arranged and form part of theoptoelectronic system used to measure the speed of rotation of disc 37.As previously mentioned with respect to FIG. 1, light emitting diode 22,positioned in opening 21 of cartridge holder 12, emits light energywhich passes through openings 20 in upper cartridge member 11a and then,if one of openings 41 in disc 37 is aligned with opening 20, throughcorresponding opening 42 in lower cartridge member 11b and opening 73(FIG. 4b) in lower holder member 12b, whereupon phototransistor 23detects the light energy. Openings 41 in disc 37 are positioned withrespect to openings 20 and 42 in cartridge 11 such that as the discrotates, light energy will be received by phototransistor 23 as a seriesof intermittent light pulses at a frequency dependent upon therotational speed of disc 37. When one of openings 41 is aligned withopening 20, light energy passes through cartridge 11 and is detected byphototransistor 23. Phototransistor 23 detects the intermittent burstsof light energy and transmits an electrical signal in synchronismtherewith to digital processor 27, thereby permitting digital processor27 to keep track of the rotational speed of disc 37 and hence the rateat which data is being written on or read from disc 37.

When cartridge 11 is assembled, disc 37 is positioned on interior majorsurface 43 of lower cartridge member 11b so that hub 38 is directlyabove opening 44. The perimeter of hub 38 is larger than the perimeterof opening 44 so that hub 38 and disc 37 are retained within cartridge11. Upper cartridge member 11a and lower cartridge member 11b snaptogether to form a protective housing for disc 37 and hub 38. When disc37 is rotated, interior major surface 43 functions as a smoothing planetherefor, i.e. air flows from the exterior of cartridge 11 throughopening 44, causing disc 37 to rise slightly above interior majorsurface 43 on a cushion of air. Interior major surface 43 includes aslightly raised portion 45 having a radius of curvature of approximatelysix inches. Raised portion 45 provides added rigidity and stability todisc 37 by causing disc 37 to conform to the curvature thereof as disc37 passes over raised portion 45 during rotation. This added stabilityis important in maintaining good head-to-disc contact and prevents disc37 from "flying away" from head 30 when head 30 penetrates as much as0.254 mm (10 mils) vertically toward disc 37. Since the remainder oflower interior major surface 43 is relatively flat, a thin cartridgeconfiguration can also be used. In addition to increasing the stabilityand rigidity of disc 37, raised portion 45 causes disc 37 to conformmore readily to the curvature of head 30 for more effective transfer ofinformation signals between head 30 and disc 37. Lower cartridge member11b further includes rectangular opening 46 with which head 30 isdisposed in registration. Head 30 is positioned at selected tracklocations on disc 37 by movement along the major axis of rectangularopening 46. The reverse sides of disc 37 and hub 38 are mirror images ofthe sides shown in FIG. 3a, thereby enabling information to be recordedon either side of disc 37.

FIG. 3b shows interior major surface 50 of upper cartridge member 11a.Major surface 50 is a substantially flat, rectangular surface,punctuated by four hump-shaped members 51 extending therefrom. As disc37 rotates, hump-shaped members 51 exert aerodynamic pressure on disc 37to bias it toward head 30 to maintain good head-to-disc contact forefffective system operation. Hump-shaped members 51 have smoothcontoured surfaces with a radius of curvature of approximately 0.375inches to eliminate vibration and flutter which can be transmitted todisc 37 and reduce the purity of video signals in particular.Hump-shaped members 51 compensate for changes in the environmentalconditions such as temperature and pressure within cartridge 11 andprevent deformation of disc 37 which can disrupt the transfer ofinformation signals between head 30 and disc 37 by destroying thehead-disc interface. As an added feature, interior major surface 50 andhump-shaped members 51 are coated with a conductive material to preventelectrostatic charge build-up on disc 37 and elsewhere within cartridge11 during system operation.

FIG. 3c shows the alignment/positioning features contained on exteriormajor surface 52 of lower cartridge member 11b. Exterior major surface52 includes a rectangular recess 53 extending perpendicularly inwardfrom end wall 54 (FIG. 3d) and elongated rectangular slots 55 extendingperpendicularly inward from opposite sides 56 of lower cartridge member11b for mating with corresponding fixtures on cartridge holder 12.

To prevent information stored on disc 37 from being erased, a writeprotect switch having a slideable button 57 is mounted in recess 54aformed in end wall 54 as shown in FIG. 3d. Button 57 projects toward themouth of recess 54a and is manually settable at first and second switchpositions, representing the WRITE ENABLE and WRITE PROTECT states,respectively.

When cartridge 11 is inserted in holder 12, the write protect switch isin abutting relationship with a spring-loaded mechanical member 58 (seeFIG. 1), which extends through opening 58a in holder 12. Referring toFIG. 3e, when button 57 is in the second position, it exerts biasingpressure on mechanical member 58 to open electrical circuit 59, whichcauses a WRITE PROTECT signal to be generated. The WRITE PROTECT signalinhibits the system from receiving further write commands from hostmachine 28 and from erasing information already recorded on disc 37.

Alternatively, to enable information to be erased and replaced with newinformation, button 57 is disengaged from mechanical member 58 and isshifted to the first (WRITE ENABLE) position, thereby releasingmechanical member 58, which protrudes into recess 54a. The releasing ofbutton 57 closes electrical circuit 59 and terminates the WRITE PROTECTsignal, thereby allowing information to be selectively erased andwritten over. The WRITE PROTECT switch permits the user to selectivelyprotect the information on disc 37 from erasure or alternatively allowit to be erased.

Cartridge Holder and Deck Alignment Features

Referring to FIGS. 4a and 4b, upper holder member 12a and lower holdermember 12b of cartridge holder 12 are shown in perspective. Majorsurface 60 of upper holder member 12a includes three openings 61, eachhaving a spring member 24 inserted therein. When cartridge 11 isinserted in holder 12, springs 24 exert downward biasing pressure oncartridge 11 to keep it in a fixed position. Another spring member 62(FIGS. 1 and 4a) is affixed to the interior end wall 63 of upper holdermember 12a for exerting a forward biasing pressure on cartridge 11 tofacilitate removal thereof. Upper holder member 12a further includesloop fasteners 64 attached to each side thereof for engaging projectionmembers 65 on either side of lower holder member 12b and locking upperholder member 12a and lower holder member 12b together to form cartridgeholder 12.

Lower holder member 12b includes a rectangular extension member 66extending perpendicularly inward from end wall 67 and a pair ofelongated detents 68 extending perpendicularly inward from oppositesides 69. When cartridge 11 is properly inserted in holder 12,rectangular extension member 66 mates with recess 53 on cartridge 11 anddetents 68 mate with respective elongated slots 55 in cartridge 11 formaintaining cartridge 11 in a fixed position. Three openings 70 locatedin major surface 71 of lower holder member 12b allow support members 25of deck 13 to extend therethrough and raise cartridge 11 slightly abovemajor surface 71 during system operation. Suport members 25 cooperatewith spring members 24 to position cartridge 11 vertically. Opening 72is in registration with opening 17 in deck 13 and opening 46 incartridge 11 for allowing access to disc 37 by head 30 and opening 73 isaligned with opening 18 in deck 13 and opening 44 in cartridge 11 forallowing motor rotational means 32 to engage hub 38 and rotate disc 37.Lower holder member 12b further includes a tongue-shaped member 74 whichextends outwardly therefrom, tongue-shaped member 74 having a tab member75 extending perpendicularly therefrom in a downward direction. Tabmember 75 has a latch member 76 affixed thereto for engaging acorresponding latch member 80 (FIG. 5b) on deck 13 for securingcartridge holder 12 to deck 13.

FIGS. 5a and 5b show cartridge holder 12, with cartridge 11 insertedtherein, mounted in deck 13. It should be noted that cartridge 11 isinsertable in holder 12 either before or after holder 12 has beenmounted in deck 13. To insert holder 12 in deck 13, extension members 15of holder 12 are inserted into slots 16. Holder 12 is then rotated 90°to a downward position as shown in FIG. 5b. When holder 12 is positionedin deck 13, support members 25 in deck 13 extend through openings 70 inholder 12 to raise cartridge 11 slightly above major surface 71 of lowerholder member 12b. Additionally, as previously mentioned, openings 72and 73 are aligned with openings 17 and 18, respectively, to ensureaccess to magnetic recording disc 37 by head 30 and motor rotationalmeans 32, respectively. When holder 12 and cartridge 11 are properlypositioned, alignment posts 26 are in abutting relationship with 90°angle surface 36 (FIGS. 1 and 3a) of cartridge 11. Deck 13 has anextension tab 81 on which latch member 80 is rotatably mounted forengaging latch member 76 of holder 12. Holder 12 is easily removeable bydisengaging latch members 76 and 80 and rotating cartridge holder 12 90°back to the vertical position shown in FIG. 5a and then lifting holder12 until extension members 15 are clear of vertical slots 16.

Referring to FIG. 6, when cartridge 11 and holder 12 are positioned indeck 13, motor rotational means 32 extends through opening 18 in deck 13and opening 73 in holder 12 to engage hub member 38. Shaft 85 extendsthrough opening 86 in hub 38 and end member 87 fits within circularprojection member 40. Radial projection 88 extending outwardly from endmember 83 engages latch member 39 extending inwardly from circularprojection member 40 to impart rotational motion to hub 38 and disc 37.When latch member 39 and radial projection 88 are in mating engagement,the outer perimeter of end member 87 is in contact with the innerperimeter of projection member 40 at a point diametrically opposed tothe engagement point of latch member 39 and radial projection 88. Thusend member 87 and hub 38 are engaged in the same position at all times,thereby providing greater accuracy in positioning disc 37 with respectto head 30. This unique coupling arrangement between hub 38 and motorrotational means 32 is described and claimed in U.S. Pat. No. 4,216,511.

Recording Head and Head Positioning System

As shown in FIG. 7, magnetic head transducer 30 is mounted on slideassembly 92 which includes shafts 93 on opposite sides thereof. Slideassembly 92 is controlled by a linear servo-motor 94 which moves slideassembly 92 and head 30 horizontally along the axis connecting A - A'.Head 30 is positioned in registration with openings 17, 72 and 46 indeck 13, holder 12 and cartridge 11, respectively, so that movement ofhead 30 along the axis A - A' moves head 30 radially across disc 37. Anoptoelectronic system is used to determine the track location of head 30at any given time. The optoelectronic system includes a shutter 95 whichis attached to slide assembly 92 and is moved in a linear fashion alongwith head 30. As seen in FIGS. 8a, 8b and 8c, shutter 95 has a pluralityof vertical apertures 96 arranged at predetermined distances along themajor axis of shutter 95. Each aperture 96 is approximately 0.127 mm (5mils) wide, the centerlines of adjacent apertures 96 being approximately0.254 mm (10 mils) apart. The optoelectronic system further includes astationary mask 97 as shown in FIG. 8b. Mask 97 includes first andsecond sets of apertures 98aand 98b, respectively. As shutter 95 movesback and forth with respect to stationary mask 97, apertures 96 areoriented in various positions with respect to first and second sets ofapertures 98a and 98b so that selected apertures of mask 97 are lined upwith selected apertures 96 of shutter 95, thereby permitting lightenergy generated by a light-emitting diode 99a to pass therethrough,while other apertures of mask 97 are not lined up with any of apertures96 of shutter 95 and are therefore blocked off by the solid portions ofshutter 95 so that light energy cannot pass therethrough. A cone-shapedmember 99b and lens 99c focus the light energy emitted by 99a to providea collimated light source. Light energy which passes through apertures98a and 98b is detected by a pair of light sensitive diodes 100a and100b, respectively, which generate respective electrical signalsindicative of the number of open apertures of each set 98a and 98b. Thesystem is responsive to these signals for generating an AC electricalsignal indicative of the relative position of head 30 with respect to aparticular track on disc 37 as shown in FIG. 16. Specifically, when head30 is positioned at one extreme of a particular track, all of theapertures in the first set of apertures 98a are aligned with apertures96, thereby permitting light to pass through, while all of the aperturesin the second set of apertures 98b are blocked off by shutter 95 so thatno light energy passes through. FIG. 8c shows shutter 95 positioned sothat all of the apertures of first set 98a are open while all of theapertures of second set 98b are closed, thereby indicating that head 30is located at one extreme of a particular recording track. At the otherextreme of the track, the opposite is true, i.e. all of the apertures offirst set 98a are blocked off while all of the apertures of the secondset 98b are open for light to pass through. When head 30 is at thecenter of the track, approximately half of the apertures of each of thesets of apertures 98a and 98b are open for light to pass through whilethe other half are closed off to light passage. As head 30 is movedradially across disc 37, an AC electrical (see, for example, FIG. 16)signal is thereby generated indicative of the position of head 30 at anygiven time. In a unique feature of the optoelectronic system justdescribed, shutter 95 and mask 97 are comprised of essentially the sameplastic material as disc 37. This enables the position of head 30 withrespect to disc 37 to be determined with greater precision bycompensating for environmental pertubations, such as changes intemperature and pressure, to which disc 37 is subject and which causedisc 37 to expand and/or contract. Shutter 95 and mask 97 are preferablyformed by cutting a piece of the plastic material at an angle ofapproximately 45° with respect to the manufacturing length of theplastic material. This is due to the fact that the thermal andhygroscopic expansion coefficients of the plastic material are differentalong the length of the material from the corresponding coefficientsalong the width of the material. The thermal and hygroscopic expansioncoefficients of shutter 95 and mask 97 represent averages of thesecoefficients along both axes of the material and thus are closer to theaverage coefficients of circular disc 37, which is formed from the samematerial. In addition, the thermal and hygroscopic time constants ofshutter 95, mask 97 and disc 37 are essentially the same. For optimumperformance, the end of shutter 95, which is positioned away from head30 is unbonded and free to move parallel to the direction of movement ofslide assembly 92. In one embodiment, performance is further enhanced bybonding mask 97 near the center of disc 37. Mask 97 is free to expandand contract away from the bonded area, parallel to the movement ofslide assembly 92.

FIGS. 9a and 9b illustrate another unique feature of the informationstorage system described herein. Magnetic head transducer 30 is affixedto ramp member 101 having an inclined surface sloping downward at a 45°angle away from head 30. Ramp member 101 is positioned between head 30and the geometric center of disc 37. When the information storage systemis not in operation, head 30 is normally positioned away from disc 37and outside of the perimeter thereof. When head 30 is moved radiallytoward disc 37 for reading and/or writing data thereon, the perimeter ofdisc 37 first contacts ramp member 101 at the lower end of the inclinedsurface and is lifted up and over the top of head 30. This preventsdamage to disc 37 due to collision with head 30 as head 30 is movedalong the disc. Furthermore, the use of ramp member 101 to move disc 37vertically into position with respect to head 30 eliminates the need foran additional electromechanical system such as a solenoid device orservo system for moving head 30 vertically with respect to disc 37 whenhead 30 is repositioned. Therefore, head 30 need only be moved linearlyalong disc 37 during system operation.

As shown in FIGS. 10a, 10b and 10c, magnetic head transducer 30 iscomprised of a relatively thin (0.20 mm or 8 mils) slice offerromagnetic material and is of substantially rectangular shape with acurved upper recording/playback surface 111. Head 30 is approximately4.06 mm (160 mils) wide in the direction X-X' and approximately 3.43 mm(135 mils) long in the direction Y-Y'. Positioned approximately 0.76 mm(3 mils) below the apex of recording surface 111 is a circular opening112 which is approximately 0.20 mm (8 mils) in diameter. Electrical coil113 is wrapped around head 30 in the direction X-X' and passes throughopening 112. Coil 113 is supplied with electrical current tomagnetically bias recording head 30 for recording and playback of dataon disc 37. Extending along the axis Y-Y' is a thin gap (1 micron) whichis comprised of front and rear gaps 114a and 114b, respectively. Frontgap 114a extends from the apex of curved surface 111 to the top ofopening 112 and rear gap 114b extends from opening 112 down to the base115 of the head 30. As part of the manufacturing process for head 30,non-magnetic material is deposited in gaps 114a and 114b to form atransducing gap. The process used for fabricating head 30 is describedin detail below.

Recording surface 111 preferably has a radius of curvature ofessentially one inch along its major axis and one-half inch along itsminor axis for optimum transfer of the information signal between head30 and disc 37 while minimizing the amount of wear on disc 37. Duringrecording and/or playback of information, a thin film of air ofapproximately 0.5 microns operates between recording surface 111 anddisc 37 to prevent wear on disc 37, but allow an intimate heat-to-discinterface. Disc 37 is flexible enough to move vertically in response tohead penetrations into disc 37, but is rigid enough not to "fly away"from head 30 when head 30 penetrates as much as 0.254 mm (10 mils)toward disc 37. An intimate heat-to-disc relationship, which is criticalfor effective system performance, is maintained over a wide variety ofhead penetrations and alignments. To further enhance signal transferbetween head 30 and disc 37, disc 37 bends slightly as it passes overhead 30 to conform more closely to the curvature of recording surface111. As shown in FIG. 10c, however, disc 37 has a lesser curvature thanhead 30 so as to prevent the edges of head 30 from digging into disc 37.

Referring to FIGS. 11a and 11b, head 30 is comprised of first and secondopposed confronting ferromagnetic pole pieces 121 and 122, respectively.Pole pieces 121 and 122 have opposing major surfaces 123 and 124,respectively, which are divided into front gap faces 123a and 124a,respectively, and rear gap faces 123b and 124b, respectively. The frontand rear gap faces of pole pieces 121 and 122 are separated by acomplementary recess 125, which forms opening 112 when pole pieces 121and 122 are affixed together.

To form the transducing gap, a non-magnetic material is formed on frontgap faces 123a and 124a at a thickness equal to the desired thickness ofthe transducing gap and a brazing alloy is deposited on rear gap faces123b and 124b at a thickness of five to ten percent greater than thethickness of the non-magnetic material. It will be evident to thoseskilled in the art that the non-magnetic material and brazing alloy maybe deposited in a variety of ways. One method of depositing thenon-magnetic material involves the deposition of a gas which containsthe non-magnetic material on front gap faces 123a and 124a. Othermethods of depositing the non-magnetic material include vacuumdeposition using direct current or radio frequency sputtering. Thenon-magnetic material is deposited at a thickness between 0.5 micron and5 microns, preferably at a thickness of approximately 1 micron.Alternatively, front gap 114a may be formed mechanically by positioninga non-magnetic shim of a thickness equal to the desired width of thetransducing gap between front gap faces 123a and 124a.

The brazing alloy, which is comprised of silver, copper and praedium, ispreferably deposited on rear gap faces 123b and 124b by RF sputtering,which is well known in the art. In RF sputtering pole pieces 121 and 122are positioned in a vacuum chamber and a target comprised of brazingalloy material is positioned thereabove. A stream of inert gas, such asArgon, is passed across the target and a DC potential or a potentialvarying at a radio frequency rate is maintained at the surface of thetarget, thereby producing an ion sheath near the target surface. Ions inthe sheath strike the target surface and cause a sputtering of thebrazing alloy material by momentum transfer, thereby depositing thematerial on rear gap faces 123b and 124b. This process can be adjustedto ensure that the desired thickness of brazing alloy material isdeposited. Pole pieces 121 and 122 are secured together with opposingmajor surfaces 123 and 124 in abutting relationship and heated to themelting temperature (850° C.) of the brazing alloy to intimately affixpole pieces 121 and 122 together to form an integral block piece 126.Block piece 126 is then sliced transversely along an axis B-B' to form aplurality of magnetic head transducers 30, each having a predeterminedthickness. It is important that the brazing alloy be deposited at athickness which is at least five percent greater than the thickness ofthe non-magnetic material deposited on the front gap faces 123a and 124ato compensate for the loss of a certain amount of the brazing alloy fromleakage and absorption during the brazing process. The result of thisprocess is the production of a magnetic head transducer 30 which has auniform gap width along the entire length of head 30 and concomitantreduction in the mechanical stress on front and rear gaps 114a and 114b.Heads 30 fabricated using this process have greatly enhanced signaloutput performance (4-6 db improvement in the output signal voltage) ascompared to head transducers formed using prior art methods in which thenon-magnetic material and brazing alloy were deposited at an equalthickness on the gap faces. This results in better fidelity of therecorded signals and less susceptibility of the information storagesystem to noise and other interference.

After one or more magnetic head transducers 30 have been sliced fromblock 126, recording surfaces 111 must be shaped to form the requiredone inch radius of curvature thereon. A unique lap and tool method isused to precisely contour large quantities of heads 30 so that all ofthe heads 30 have a uniform shape. Individual heads 30 are secured torespective flat surfaces of a cone-shaped holder 131 as depicted inFIGS. 12a and 12b and holder 131, with heads 30 attached thereto, isplaced in a hemispherical positioning tool, such as transfer block 132,having a concave surface 133 with a radius of curvature of one inch.Selected flat surfaces of holder 131 are oriented so that they lie inplanes which are perpendicular to other flat surfaces on holder 131.Spacer means 134 is provided to retain holder 131 in a predeterminedposition in transfer block 132 so that recording surfaces 111 of heads30 are tangent to concave surface 133 and in abutting relationshiptherewith. The orientation of heads 30 with respect to concave surface133 is further adjusted by sliding heads 30 along their respective flatsurfaces until the desired position is achieved. When each head 30 isproperly positioned, the axis Y-Y' extending along the length of head 30(FIG. 10a) is substantially orthogonal to both recording surface 111 andconcave surface 133. Furthermore, when heads 30 are properly positioned,the axis Y-Y' extending through a pair of heads 30 which are affixed tomutually perpendicular flat surfaces form one inch legs of an isocelesright triangle having a base of 1.414 inches extending between therespective points of intersection of the two heads 30 with concavesurface 133 as shown by dotted lines in FIG. 12a. Therefore, spacermeans 134 can be used to properly position heads 30 by adjusting theposition of holder 131 and heads 30 so that the aforementioned points ofintersection are 1.414 inches apart.

When heads 30 are properly positioned, holder 131 is removed andpositioned in a rotatable hemispherical grinding apparatus 135 having aconcave surface 136 with a one inch radius of curvature so thatrecording surfaces 111 of heads 30 are in abutting relationshiptherewith. Heads 30 are held in a fixed position while concave surface136 is rotated by motor 137, thereby mechanically grinding recordingsurface 111 to form approximately the desired one inch contour thereon.To further refine the contouring, recording surface 111 is polished by aseries of rotatable hemispherical polishing tools, each having a concavesurface with a one inch radius of curvature, in a manner similar to thatdescribed with respect to grinding apparatus 135. This provides moreprecise contouring of recording surface 111 and removes rough spots andother irregularities thereon. The above-described lap and tool method iseffective in forming large quantities of precisely contoured magnetichead transducers 30 having uniformly contoured recording surfaces 111.Heads 30 contoured using this method are suitable for use in highperformance, high density information storage systems such as the systemdisclosed herein.

In a further feature of the unique information storage system, recordingof information signals is accomplished with fewer errors by varying thewrite current supply to recording head 30 in dependence upon theparticular recording track on which data is being recorded. Magneticrecording disc 37 is divided into four quadrants, RW1, RW2, RW3 and RW4,beginning at the perimeter and moving radially inward to the center, asshown in FIG. 13. The first quadrant is comprised of tracks 0-20, thesecond, tracks 21-40, the third, tracks 41-60 and the fourth, tracks61-79. As shown in FIG. 14, host machine 28, such as a computing system,determines the particular track on which data is to be recorded andsends a nine bit TRACK COUNT signal to digital processor 27 selectingthe particular track on which data is to be written. In responsethereto, digital processor 27 sends a TRACK CLOCK signal back to hostmachine 28 indicating it has received one bit of the TRACK COUNT signal.Digital processor 27, after positioning head 30 on the particular track,determines the particular quadrant in which the track is located andgenerates an output signal on one of four output lines R5, R6, R7 and R8to turn on a selected one of four switching transistors 143a, 143b, 143cand 143d.

Each transistor has a respective resistor 144a, 144b, 144c and 144d,each having a discrete resistance value, in series therewith for varyingthe current input to recording amplifier 145. Transistors 143a, 143b,143c and 143d, together with their associated resistors 144a, 144b, 144cand 144d, provide four parallel electrical paths connecting power supply146 with head 30. The particular electrical path which is activated bydigital processor 27 is a function of the quadrant in which the selectedtrack is located. Transistor 143a is turned on whenever the selectedtrack is located in the first quadrant, i.e. tracks 0-20, transistor143b is turned on when the selected track is located in the secondquadrant comprising tracks 21-40 and so forth. For example, if computingsystem 28 selects track 17 on which to write data, digital processor 27sends an output signal via output terminal R5 to turn on transistor 143aand allow current to pass therethrough and through resistor 144a torecording amplifier 145 and thence a head 30. Amplifier 145 converts theDC voltage supplied by power supply 146 to an AC voltage supply for head30. The information to be recorded on disc 37 is transmitted directlyfrom host machine 28 via amplifier 145 to head 30. If, on the otherhand, host machine 28 selects track 35, which is in the second quadrant,digital processor 27 activates switching transistor 143b which allowscurrent to flow therethrough and through resistor 144b to amplifier 145and head 30. Because resistor 144b has a different resistance value fromresistor 144a, the current supplied to head 30 for writing informationon track 35 is different from that supplied to head 30 when informationis being written on track 17.

Optimum performance is obtained by supplying the greatest amount ofwrite current to head 30 when data is being recorded on tracks in thefirst quadrant (the outermost tracks 0-20). This is due to the fact thatthe outer portion of magnetic recording disc 37 is moving at a greatervelocity than the inner portion and therefore the data density is lesson the outside tracks when the rate at which data is recorded isconstant. When the data density is decreased, a given amount of data isbeing distributed over a large annular region of disc 37. The outertracks are therefore more susceptible to the occurrence of inflectionpoints, which produce errors in the information signal. On the innertracks, such as, for example, tracks 61-79 in the fourth quadrant, thedata density is greater than on the outside tracks so that inflectionpoints are less likely to occur. Therefore, a lesser amount of writecurrent supply is required. The write current is therefore varied as afunction of track location by choosing the resistance values so thatresistor 144d has the largest resistance to ensure that the innermosttracks (fourth quadrant) receive the least amount of write current andresistor 144a has the least resistance to ensure that the outermosttracks (first quadrant) receive the greatest amount of write current.This arrangement not only reduces errors in the information signal, butalso provides improved system fidelity and enables a single head 30 tobe used for recording, playback and erasure. Table I lists theinstruction codes stored in digital processor 27 for executing theabove-described write current routine.

The system depicted in FIG. 15 expedites the movement of head 30 fromone track to another on disc 37 and maintains head 30 in a predeterminedposition with respect to the centerline of a selected track. Movementsof head 30 are optically detected by optoelectronic system 151, whichgenerates an AC signal indicative thereof, as shown in FIG. 16. The zerocrossing points of the signal at the 0 and 10 positions on thehorizontal axis of FIG. 16 correspond to the respective centerlines ofadjacent tracks of disc 37. The vertical axis represents the voltageamplitude of the signal. When the amplitude of the AC signal reaches athreshold value, V_(t), linear amplifier and logic control circuit 152generates a SNSRNUL signal until the amplitude drops below the thresholdvalue.

Digital processor 27 controls the repositioning of head 30 from onetrack to another by generating a series of ACCELERATION and DECELERATIONcontrol signals via loop state control lines 153. Analog amplifier 152is responsive thereto for controlling linear servomotor system 94 tomove head 30 in accordance with the ACCELERATION and DECELERATIONsignals from one position to another along disc 37. The repositioningsequence is begun when host machine 28 transmits a TRACK COUNT signalindicative of a selected track location to digital processor 27, whichcomputes the number of tracks between the present location of head 30and the selected track location and the direction in which head 30 mustbe moved. If head 30 is to be moved to a position at least 16 tracksaway from its present location, head 30 is first moved in oneeight-track increment and then in single track increments for theremaining eight or more tracks up to a maximum of 15 single trackincrements. If head 30 is to be repositioned fewer than 16 tracks, it ismoved in single track increments only. Digital processor 27 isprogrammed so that whenever head 30 is moved one or more increments ofeight tracks each the eight track increments are followed by at leasteight, but not more than 15 single track increments. The relationshipbetween the number of tracks which head 30 must traverse and the numberof eight-track increments through which head 30 is moved to arrive atthe selected track is expressed as follows:

    (M+1)·8≦N<(M+2) 8

N=total number of tracks head 30 must negotiate

M=number of eight track increments through which head 30 is moved.

Thus head 30 is moved M increments of eight-tracks each when N isgreater than or equal to (M+1)·8.

For example, if head 30 is to be moved from track 5 to track 28 (23tracks), it will be moved in one eight-track increment followed by 15single track increments, as shown in FIG. 17a. However, if head 30 is tobe moved 24 tracks, from track 5 to track 29, head 30 will be moved intwo eight-track increments followed by eight single track increments, asshown in FIG. 17b.

FIG. 16 shows the relationship of the ACCELERATION and DECELERATIONsignals generated by digital processor 27. When head 30 is being movedin single track increments, the ACCELERATION signal is generated forapproximately one-half of each track, followed by the DECELERATIONsignal for the other half. This causes head 30 to alternately accelerateand decelerate across each track, resulting in the small sawtoothvelocity patterns shown in FIG. 17. When head 30 is being moved in aneight-track increment, the ACCELERATION signal is generated forapproximately 4.5 tracks, followed by the DECELERATION signal for theremaining 3.5 tracks. This results in the large sawtooth velocitypatterns of FIG. 17.

By moving head 30 in one or more increments of eight tracks each, head30 is repositioned faster on selected tracks, thereby improving systemresponse time. Those skilled in the art will appreciate that digitalprocessor 27 may be programmed to move head 30 in multi-track incrementsother than eight-track increments. Table II lists the instruction codesstored in digital processor 27 for controlling the repositioning of head30 on disc 37.

When head 30 is in position on a selected track, analog amplifier 152maintains head 30 within a predetermined region on either side of thecenterline of the recording track. Analog amplifier 152 is responsive tothe AC position signal generated by optoelectronic system 151 forgenerating a restoring force to return head 30 to its centerline or homeposition. The farther head 30 strays from the centerline, the greaterthe amplitude of the AC position signal and the greater the restoringforce. Preferably, head 30 is constrained to move within a 0.025 mm (1mil) region on either side of the centerline. When head 30 deviates onemil or more from the centerline, analog amplifier 152 generates aSNSRNUL signal which causes digital processor 27 to go into an ERRORroutine, thereby preventing further recording or playback of data whilereturning head 30 to its proper position.

When it is desired to erase information from a particular track on disc37, host machine 28 transmits an ERASE command signal to digitalprocessor 37 as shown in FIG. 18a. Because each recording track is only0.203 mm (8 mils) wide, head 30 cannot effectively erase the entire areaof the track if it remains positioned at the centerline.

To ensure that all remnants of the information signal are erased,digital processor 27, in response to the ERASE command signal (ERASE=0),generates LEAN A and LEAN B control signals (FIG. 18b), each of which istransmitted as a three bit binary coded signal via loop state controllines 153 to analog amplifier 152. The LEAN A and LEAN B signalsintroduce position biasing signals of +1 volt and -1 volt, respectively,into the control loop, thereby causing analog amplifier 152 to maintainhead 30 at a position which is offset a distance of 0.025 mm (1 mil)from the centerline of the track on either side thereof. When either theLEAN A or LEAN B signal is being generated, the threshold of the SNSRNULsignal is raised from 1 volt to 1.5 volts, which is equivalent toraising the maximum displacement of head 30 from 0.025 mm (1 mil) to0.38 mm (1.5 mils). This prevents the SNSRNUL signal from going high andtriggering the ERROR routine when head 30 is moved or "leaned" to theoffset positions for erasing information.

When the LEAN A signal is generated, head 30 is displaced 0.025 mm (1mil) from the centerline position (zero position in FIG. 18c) in adirection toward the geometric center of disc 37 so that head 30 iscentered at the -1 mil position. A 3 MHz electrical signal is thensupplied to head 30 to erase information in an 0.8 mil (0.203 mm) wideregion between the -5 mil and +3 mil positions. When the LEAN B signalis transmitted, head 30 is displaced in a direction away from thegeometric center of disc 37 to the +1 mil position. The 3 MHz erasesignal is again applied to head 30 to erase information in the 8 milwide band between the -3 mil and +5 mil positions. Thus the entire 10mil (0.254 mm) wide recording track is eraseable using this technique.If head 30 strays 1.5 mils (0.038 mm) or more from the centerline, theSNSRNUL signal goes high which activates the ERROR routine (see TableIV) to prevent head 30 from erasing information on adjacent tracks.

When the ERASE command signal goes low (ERASE=1), digital processor 27outputs a TRUENUL instruction via loop state control lines 153 to returnhead 30 to its centerline position and normal operation is resumed.Table III lists the instruction codes stored in digital processor 27 forexecuting the ERASE routine.

In order to remove debris and other contaminants from recording head 30which interfere with the head-to-disc interface and prevent effectivetransfer of information signals, a special head cleaning cartridge 161(FIGS. 19a and 19b) is inserted in the information storage system inlieu of the normal cartridge 11 that is used for recording and playbackof information. Head cleaning cartridge 161 contains a flexible sheet ofabrasive material 161a (FIG. 19c) and has substantially the same sizeand shape as recording cartridge 11, including rectangular opening 161bwhich is disposed in registration with head 30 when cleaning cartridge161 is installed. Abrasive sheet 161a has the same size and shape asdisc 37 (see FIG. 3a) and is comprised of the same flexible plasticmaterial. Rather than having a magnetic flux-responsive coating thereon,as does disc 37, abrasive sheet 161a has a rough surface with anabrasiveness on the order of 0.3 microns to clean and polish recordingsurface 111. Cleaning cartridge 161 includes an additional circularopening 162 located at one corner of lower major surface 163 so that theinformation storage system can discriminate between recording cartridge11 and cleaning cartridge 161. When no cartridge is inserted, switch 164is open and switch 165 is closed. When recording cartridge 11 isinserted in holder 12 of the information system, it exerts downwardbiasing pressure on both switches 164 and 165 to close switch 164 andand open switch 165, thereby transmitting a binary coded signal todigital processor 27 indicative of the fact that recording cartridge 11is installed in the system. When head cleaning cartridge 161 isinserted, it exerts biasing pressure on switch 164, only to close withswitch 164. Switch 165 remains in a closed position, because opening 162is positioned directly above mechanical member 165a of switch 165.Mechanical member 165a extends into opening 162 and remains in areleased or extended position. Digital processor 27 receives a uniquebinary coded signal indicating that switches 164 and 165 are closed,thereby informing digital processor 27 that head cleaning cartridge 161has been inserted.

Referring to FIG. 19c, when digital processor 27 receives the binarycoded signal indicating that head cleaning cartridge 161 is positionedin the system, it executes a head cleaning routine in accordance withthe instruction set stored therein. Digital processor 27 controls analogamplifier 152 to activate linear servomotor 94 and move head 30 back andforth radially across the abrasive sheet 161a rapidly for 20 seconds,thereby polishing recording surface 111 to remove debris and otherforeign matter therefrom. Abrasive sheet 161a is flexible and bends toconform more readily to the shape of head 30, thereby providing a morethorough cleaning of the entire recording surface 11. The inside of headcleaning cartridge 161 is similar to the inside of recording cartridge11 as shown in FIG. 3 and includes four hump-shaped members 51 andraised portion 45 on the lower surface to keep abrasive sheet 161a incontact with head 30. The two parallel hump-shaped members 51 positionedabove opening 46 in head cleaning cartridge 161 have a more pronouncedcurvature than the corresponding members 51 in recording cartridge 11 tocause abrasive sheet 161a to bend to conform to the shape of head 30 formore effective cleaning.

When the cleaning routine is in process, a COMPLETE signal istransmitted by digital processor 27 via line 169 to host machine 28,indicating that the system is occupied. Switch 164 transmits anelectrical signal to host machine 28 via line 170 indicating that acartridge has been inserted in the system. When abrasive sheet 161a isrotated and the cleaning routine begins, light emitting diode 171 isturned on, indicating that the system is in operation. Upon completionof the cleaning routine, head cleaning cartridge 161 is removed. Table Vlists the instruction codes stored in digital processor 27 for executingthe head cleaning routine.

Various embodiments of the invention have now been described in detail.Since it is obvious that many additional changes and modifications canbe made in the above-described details without departing from the natureand spirit of the invention, it is understood that the invention is notto be limited to said details except as set forth in the appendedclaims. ##SPC1## ##SPC2## ##SPC3## ##SPC4## ##SPC5## ##SPC6## ##SPC7##

I claim:
 1. A method of shaping respective recording/playback surfacesof a plurality of magnetic head transducers to form contoured surfaceshaving a predetermined curvature, said method comprising the stepsof:(a) providing holder means and attaching a first head transducer to afirst relatively flat surface of said holder means so that a majorsurface of said first head transducer is parallel to the firstrelatively flat surface; (b) attaching a second head transducer to asecond relatively flat surface of said holder means so that a majorsurface of said second head transducer is parallel to the secondrelatively flat surface, said second relatively flat surface lying in aplane which is substantially orthogonal to a plane in which the firstrelatively flat surface lies; (c) providing positioning means having aconcave surface with a radius of curvature equivalent to thepredetermined curvature for receiving said holder means with said firstand second head transducers attached thereto; (d) disposing therecording/playback surfaces of said first and second head transducers inabutting relationship with said concave surface and at a predetermineddistance apart which is substantially equal to the hypotenuse of anisoceles right triangle, the legs of which are each of a lengthequivalent to the radius of curvature of the concave surface, so thatrespective axes which are orthogonal to said recording/playback surfacesare also orthogonal to said concave surface; (e) providing shaping meanshaving a concave surface with a radius of curvature equivalent to thepredetermined curvature and placing said recording/playback surfaces incontact with said concave surface of said shaping means; and (f)providing relative motion between said concave surface of said shapingmeans and said recording/playback surfaces so that saidrecording/playback surfaces are contoured to the predeterminedcurvature.
 2. The method according to claim 1 wherein saidrecording/playback surfaces are shaped to form a one inch radius ofcurvature thereon.
 3. The method according to claim 1 wherein saidrecording/playback surfaces are contoured by mechanically grinding therecording/playback surfaces to approximately the predetermined curvatureand polishing the recording/playback surfaces to form smooth contouredsurfaces having the predetermined curvature.
 4. The method according toclaim 1 wherein said step of disposing said recording/playback surfacesof said first and second head transducers is comprised of the followingsubsteps:(i) selectively disposing spacer means of predeterminedthickness between said holder means and said concave surface of saidpositioning means; (ii) moving said first and second head transducersalong said respective axes until said recording/playback surfaces are incontact with the concave surface, the thickness of said spacer meansbeing selected so that said recording/playback surfaces are separated bysaid predetermined distance; and (iii) securing said first and secondtransducers to said respective first and second relatively flat surfacesto maintain said first and second head transducers in respective fixedpositions relative to said holder means.
 5. The method according toclaim 1 wherein said holder means is equipped with a plurality of saidrespectively flat surfaces, each of said flat surfaces for accomodatingone head transducer, and a plurality of head transducers are attached torespective flat surfaces of said holder means, the respectiverecording/playback surfaces of said plurality of head transducers beingshaped at the same time to form uniformly contoured surfaces having saidpredetermined curvature.
 6. A method of positioning a magnetic headtransducer to allow a recording/playback surface of the head transducerto be selectively contoured to a predetermined curvature, comprising thesteps of:(a) providing holder means and attaching said head transducerto a first relatively flat surface of said holder means so that themajor surface of said head transducer is parallel to the firstrelatively flat surface; (b) providing a cooperating member ofsubstantially the same dimensions and shape as said head transducer andattaching said cooperating member to a second relatively flat surface sothat a corresponding major surface of cooperating member is parallel tosaid second relatively flat surface; (c) providing positioning meanshaving a concave surface with a radius of curvature equivalent to thepredetermined curvature for receiving said holder means with said headtransducer and cooperating member attached thereto; (d) disposing saidrecording/playback surface and a corresponding surface of saidcooperating member in abutting relationship with said concave surfaceand at a predetermined distance apart, said predetermined distance beingselected so that an axis which is orthogonal to the recording/playbacksurface of said head transducer is also substantially orthogonal to theconcave surface.
 7. The method according to claim 6 wherein said headtransducer and said cooperating member are first and second magnetichead transducers, respectively, having respective recording/playbacksurfaces, said first and second magnetic head transducers being attachedto respective first and second relatively flat surfaces which extendoutwardly from diametrically opposed positions on a cylindrical surfaceof said holder means, said first and second flat surfaces lying inmutually perpendicular planes so that said predetermined distance isequivalent to the hypotenuse of an isoceles right triangle, the legs ofwhich are each of a length equivalent to the radius of curvature of theconcave surface.
 8. The method according to claim 7 wherein said step ofdisposing the recording/playback surfaces of said first and second headtransducers is comprised of the following substeps:(i) selectivelydisposing spacer means of predetermined thickness between said holdermeans and said concave surface; (ii) moving said first and second headtransducers along respective axes which are orthogonal to saidrecording/playback surfaces until said recording/playback surfaces arein contact with the concave surface, the thickness of said spacer meansbeing selected so that said recording/playback surfaces are separated bysaid predetermined distance; and (iii) securing said head transducers tosaid respective first and second relatively flat surfaces to maintainsaid head transducers in fixed positions relative to said holder means.